Gratings with variable depths for waveguide displays

ABSTRACT

A manufacturing system for fabricating self-aligned grating elements with a variable refractive index includes a patterning system, a deposition system, and an etching system. The manufacturing system performs a lithographic patterning of one or more photoresists to create a stack over a substrate. The manufacturing system performs a conformal deposition of a protective coating on the stack. The manufacturing system performs a deposition of a first photoresist of a first refractive index on the protective coating. The manufacturing system performs a removal of the first photoresist to achieve a threshold value of first thickness. The manufacturing system performs a deposition of a second photoresist of a second refractive index on the first photoresist. The second refractive index is greater than the first refractive index. The manufacturing system performs a removal of the second photoresist to achieve a threshold value of second thickness to form a portion of an optical grating.

BACKGROUND

The present disclosure generally relates to waveguide displays, andspecifically to manufacturing optical grating elements with a variabledepth and duty cycle.

Near-eye light field displays project images directly into a user's eye,encompassing both near-eye displays (NEDs) and electronic viewfinders.Conventional near-eye displays (NEDs) generally have a display elementthat generates image light that passes through one or more lenses beforereaching the user's eyes. Additionally, NEDs in augmented realitysystems are typically required to be compact and light weight, and toprovide large exit pupil with a wide field-of-vision for ease of use.However, designing a conventional NED with materials of desired opticalproperties often results in a very low out-coupling efficiency of theimage light received by the user's eyes due to mismatch in the size andshape of the grating element. While conventional lithography methods canproduce optical grating elements with a variable duty cycle, suchmethods are incapable of modulating the height of the optical grating.Accordingly, there is a lack of a manufacturing system to fabricateoptical grating elements with variable depths and duty cycles with ahigh throughput.

SUMMARY

Embodiments relate to a method of manufacturing an optical grating foran optical waveguide. In some embodiments, the manufacturing system forfabricating the optical grating includes a patterning system, adeposition system, and an etching system. The manufacturing systemperforms a lithographic patterning of one or more photoresists depositedover a substrate. The manufacturing system performs a deposition of atleast one of: an etch-compatible film, a metal, a photoresist, or somecombination thereof.

The manufacturing system performs a lithographic patterning of a firstphotoresist deposited over a substrate to form a pattern and themanufacturing system transfers the pattern into an underlying hard mask.The manufacturing system performs a deposition of a second photoresiston the patterned hard mask. The manufacturing system performs alithographic patterning of the second photoresist to create a modifiedsecond photoresist with a plurality of heights relative to thesubstrate. The manufacturing system performs a pattern transfer onto thesubstrate based on the plurality of heights in the modified secondphotoresist and the pattern defined by the hard mask to form ananoimprint mold including at least a plurality of different etch depthsand one or more duty cycles. In some configurations, the manufacturingsystem performs a transfer of a pattern in the nanoimprint mold onto anoptical waveguide to form an optical grating with a plurality ofdifferent etch depths and one or more duty cycles. In someconfigurations, the second photoresist is a gray-scale photoresistlithographically patterned using a gray-scale mask.

In some embodiments, the second photoresist is a gray-scale photoresistlithographically patterned using a gray-scale mask. The manufacturingsystem fabricates the gray-scale mask by performing a deposition of ametal layer over a second substrate and adjusting a thickness of a metallayer based on an erosion process performed with a 1D ion beam movingover the metal layer. In another embodiment, the manufacturing systemfabricates the gray-scale mask with a threshold number of layers of asecond material. The manufacturing system performs a deposition of athird photoresist over the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a manufacturing system, in accordance withone or more embodiments.

FIG. 2A is a flowchart illustrating the process of fabricating gratingelements with a variable height performed by the manufacturing system ofFIG. 1, in accordance with one or more embodiments.

FIG. 2B is a flowchart illustrating the process of fabricating gratingelements with a variable height and one or more duty cycles performed bythe manufacturing system of FIG. 1, in accordance with one or moreembodiments.

FIG. 2C is a flowchart illustrating the process of fabricating gratingelements with a variable height and one or more duty cycles performed bythe manufacturing system of FIG. 1, in accordance with one or moreembodiments.

FIG. 3A-C illustrate a process of creating grating elements with avariable height by the manufacturing system of FIG. 1, in accordancewith one or more embodiments.

FIG. 4 is an illustration of a laser ablation process for fabricating agray-scale mask using the manufacturing system of FIG. 1, in accordancewith one or more embodiments.

FIG. 5A is an illustration of a layer-by-layer deposition processfabricating a gray-scale mask using the manufacturing system of FIG. 1,in accordance with one or more embodiments.

FIG. 5B is an illustration of a layer-by-layer deposition processfabricating a gray-scale mask using the manufacturing system of FIG. 1,in accordance with one or more embodiments.

FIG. 6A is an illustration of a layer-by-layer etching processfabricating a gray-scale mask using the manufacturing system of FIG. 1,in accordance with one or more embodiments.

FIG. 6B is an illustration of a layer-by-layer etching processfabricating a gray-scale mask using the manufacturing system of FIG. 1,in accordance with one or more embodiments.

FIG. 7 is an illustration of a process of creating an optical gratingwith a variable height and/or one or more duty cycles using themanufacturing system of FIG. 1, in accordance with one or moreembodiments.

FIG. 8 is an illustration of a process of creating an optical gratingwith a variable height and/or one or more duty cycles using themanufacturing system of FIG. 1, in accordance with one or moreembodiments.

FIG. 9 is a diagram of a near-eye-display (NED) with optical gratingfabricated using the manufacturing system of FIG. 1, in accordance withone or more embodiments.

The figures depict various embodiments of the present invention forpurposes of illustration only. One skilled in the art will readilyrecognize from the following discussion that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles of the invention described herein.

DETAILED DESCRIPTION

Overview

A manufacturing system for creating variable etch depth features inoptical grating elements for optical waveguide displays. Whileconventional lithographic techniques (e.g. photolithography,electron-beam lithography, etc.) produce optical gratings with a highlycustomizable duty cycle by varying the size and/or spacing of suchoptical gratings, these lithographic techniques are not capable ofmodulating the vertical dimension (i.e. etch depth) of the opticalgrating relative to the substrate over the entire area of the substrate.Variable etch depth features can, e.g., control power being provided tovarious diffraction orders in, e.g., a diffraction grating. Themanufacturing system uses a pattern (e.g., Chrome) on an etch-compatiblefilm (e.g., Quartz) to create uniform etch depth across theetch-compatible film. A grayscale photomask is used to create amodulated photoresist across the etch-compatible film, that whendeveloped, creates variable etch depth features. In alternateconfigurations, the manufacturing system performs the whole processdirectly on glass to form etched waveguides instead of making ananoimprint etch-compatible film.

In some configurations, the manufacturing system performs a lithographicpatterning of the third photoresist based on an exposure process usingat least one of a scanning laser beam and/or a digital micro-mirrorbased exposure. The manufacturing system performs a deposition of thesecond material that blocks ultra-violet radiation with the thirdphotoresist acting as the lift-off mask. The manufacturing systemperforms a removal of the lithographically patterned third photoresistto form a gray-scale mask with varying amounts of location specificsecond material that absorbs UV light.

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

FIG. 1 is a block diagram of a manufacturing system 100, in accordancewith one or more embodiments. The manufacturing system 100 is a set ofsystems that produces optical grating elements with an adjustable heightand/or duty cycles in a waveguide display. In one embodiment, themanufacturing system 100 produces a gray-scale photomask based on alaser ablation process, as described below with reference to FIG. 4. Thegray-scale photomask is used to fabricate optical gratings withdifferent etch depths (e.g. few hundred nanometers to a few microns),one or more duty cycles (e.g. 10 percent to 90 percent), or somecombination thereof. Such optical gratings cannot be formed usingconventional lithographic techniques. In another embodiment, themanufacturing system 100 produces a gray-scale photomask based on alayer-by-layer deposition process, as described below with reference toFIG. 5A-B. In yet another embodiment, the manufacturing system 100produces a gray-scale photomask based on a layer-by-layer etchingprocess, as described below with reference to FIG. 6A-B. Someembodiments of the manufacturing system 100 have system components thanthose described here. Similarly, the functions can be distributed amongthe system components in a different manner than is described here. Themanufacturing system 100 includes a patterning system 110, a depositionsystem 120, an etching system 130, or some combination thereof. Themanufacturing system 100 may be similar to a system of fabricatingdevices used to form an integrated circuit, and may include suchcomponents as an etching component, a thin film manufacturing component,an oxidation component, and so on. In some embodiments, themanufacturing system 100 includes a controller (not shown here) thatcontrols some or all of the systems in the manufacturing system 100.

The patterning system 110 is a system that performs a patterning of asubstance formed on a substrate creating a change in geometry of thesubstance. In some embodiments, the patterning system 110 includes aconvection oven, a hot plate, a cool plate, an infrared lamp, a waferspinner, a mask aligner, an exposure system, a wet bench based developersystem, or some combination thereof. In one example, the patterningsystem 110 includes a pair of convection ovens for processing batches ofwafers through hard and soft baking for dehydration purposes at atemperature in the range of 150-200° C., a programmable wafer spinner, acontact-type mask aligner, and an exposure system with a mercury sourceof intensity close to 25 mW/cm².

In another embodiment, the patterning system 110 includes equipmentperforming at least one of: a laser ablation, an electron beamlithography, an interference lithography, a multi-photon lithography, ascanning probe lithography, or some combination thereof. In a firstexample, the patterning system 110 is based on electron beam lithographyin which a focused beam of electrons performs a scanning of a desiredshape on a surface covered with an electron-sensitive film. The focusedelectron beam changes the solubility of the electron-sensitive filmresulting in a selective removal of either the exposed or unexposedregions of the electron-sensitive film by immersing in a solvent. In asecond example, the patterning system 110 is based on interferencelithography in which an interference pattern consisting of a periodicseries of fringes representing intensity minima and maxima between twoor more coherent light waves is set up and recorded in a light sensitivematerial. In some configurations, the patterning system 110 includes oneor more devices performing two-beam interference lithography, athree-beam interference lithography, a four-beam interferencelithography, a multi-wave interference lithography, or some combinationthereof. Accordingly, the patterning system 110 may perform alithographic patterning of an array of patterns with a hexagonalsymmetry, a rectangular symmetry, an aperiodic pattern with a definedspatial frequency spectrum, or some combination thereof. In a thirdexample, the patterning system 110 is based on multi-photon lithographyin which a negative-tone or positive-tone photoresists is illuminatedwith light from a laser of well-defined wavelength without the use ofany complex optical systems. The multi-photon lithography process isbased on a multi-photon absorption process in a light-sensitive materialthat is transparent at the wavelength of the laser for creating thelithographic pattern. By scanning and properly modulating the laser, achemical change occurs at the focal spot of the laser and can becontrolled to create an arbitrary three-dimensional periodic ornon-periodic pattern. In a fourth example, the patterning system 110 isbased on scanning probe lithography in which a scanning probe microscopeis used for directly writing the desired lithographic pattern on alight-sensitive material using heat, chemical reaction, diffusion,oxidation, electrical bias, mechanical force, or some combinationthereof. In some configurations, the patterning system 110 includes oneor more devices performing lithographic patterning on a photo-sensitivematerial at different locations simultaneously using different types ofscanning probe microscope in a parallel fashion for high volumemanufacturing.

In alternate embodiments, the patterning system 110 includes animprinting system that performs a mechanical stamping of a pattern on asubstrate. In one example, the imprinting system performs a transfer ofa pattern onto the substrate based on a removal of a residual polymericlayer and a subsequent removal of features imprinted into the patternedsubstrate. The patterning system 110 includes a thermal imprintingsystem, an ultraviolet imprinting system, a jet and flash imprintingsystem, a reverse imprinting system, or some combination thereof. Thethermal imprinting system is a system that applies a mechanical force ona pre-heated stamp against a thermoplastic polymer that was previouslyspin-coated on the substrate. The ultraviolet imprinting system is asystem that applies an ultraviolet radiation on a low-viscosity,UV-curable polymer (e.g. PDMS, HSQ) to cross-link the polymer followedby releasing the etch-compatible film from the substrate. The jet andflash imprinting system is a system that dispenses the polymer on thesubstrate through one or more ink-jets at a low pressure and temperaturecompared to the thermal imprinting system and the ultraviolet imprintingsystem. The reverse imprinting system is a system that coats a polymerdirectly onto a template and releases the patterned substrate by tuningthe surface energies of the template and the substrate.

The deposition system 120 is a system that adds one or more thin filmsof materials on the substrate patterned by the patterning system 110. Insome embodiments, the deposition system 120 adds a plurality of thinfilms of materials to form the stack with a gradient of refractiveindices along any direction based on the differences between therefractive indices of two adjacent layers of materials. The depositionsystem 120 adds the thin films of materials on the substrate based on aphysical vapor deposition, a chemical vapor deposition, an atomic layerdeposition, a spin coating system, or some combination thereof, asdescribed below in conjunction with FIG. 5. In some configurations, thedeposition system 120 deposits thin films of materials selected from agroup consisting of: an organic polymer, a dielectric layer, or somecombination thereof. For example, the deposition system 120 deposits oneor more layers of silicon di-oxide, SSQ derivatives, an organic polymer,titanium di-oxide, hafnium di-oxide, silicon nitride, or somecombination thereof.

The deposition system 120 may include an electron-beam evaporator, amagnetron sputter, a reactive sputter, a low pressure chemical vapordeposition (LPCVD) reactor, a plasma-enhanced chemical vapor deposition(PECVD) reactor, an atomic layer deposition (ALD) reactor, or somecombination thereof. The electron-beam evaporator is based on a form ofphysical vapor deposition in which a target anode is bombarded with anelectron beam given off by a charged tungsten filament under highvacuum. The electron beam causes atoms from the target to transform intothe gaseous phase. The atoms from the target then precipitate into asolid form, coating everything in the vacuum chamber within line ofsight with a thin layer of the anode material. The magnetron sputteruses a strong electric and magnetic fields to confine charged plasmaparticles close to the surface of the sputter target. In a magneticfield, electrons follow helical paths around magnetic field lines,undergoing more ionizing collisions with gaseous neutrals near thetarget surface than would otherwise occur. The reactive sputter is basedon the sputtered particles undergoing a chemical reaction before coatingthe substrate. The chemical reaction that the particles undergo is witha reactive gas introduced into the sputtering chamber such as oxygen ornitrogen. The low pressure chemical vapor deposition (LPCVD) reactor isbased on a chemical process at a pressure lower than the atmosphericpressure in which the substrate is exposed to one or more volatileprecursors which react and/or decompose on the substrate surface toproduce the desired deposit. The plasma-enhanced chemical vapordeposition (PECVD) is based on a chemical process that utilizes plasmato enhance the chemical reaction rates of the volatile precursorsallowing deposition at lower temperatures. In some configurations, thedeposition system 120 performs the deposition of organic coatings suchas plasma polymers at a temperature relatively lower than the roomtemperature. The atomic layer deposition (ALD) reactor is based on achemical process in which alternating monolayers of two elements aredeposited onto a substrate by alternatively pulsing the chemicalreactants in a reaction chamber and then chemisorbing in a saturatedmanner on the surface of the substrate, forming a chemisorbed monolayer.In some configurations, the deposition system 120 includes a controller(not shown here) that controls a number of cycles of pulsing theprecursors into the reaction chamber, the deposition time for eachpulsing, and the time for purging the reaction chamber after eachpulsing.

The deposition system 120 may also deposit an etch-compatible film of atarget value of thickness over a substrate. The etch-compatible film maybe composed of materials including, but not restricted to metals ormetallic compounds (e.g. TiOx, WC, W, Cr, TiN, etc.), silicon containingmaterials (e.g. SiO2, Si3N4, SiON, SiC), carbon containing materials(e.g. amorphous carbon, diamond like carbon, spin on carbon) epoxyresins (e.g. SU-8), novolac resins, etc.

The etching system 130 is a system that removes one or more thin filmsof materials deposited on the substrate patterned by the patterningsystem 110. The etching system 130 is based on a physical process, achemical process, or some combination thereof. The etching system 130selectively removes a first set of one or more thin films of materialsat a different rate of removal when compared to a second set of one ormore thin films of materials in a multi-layered stack of materialsdeposited on the substrate. The etching system 130 includes a wet bench,an ion milling module, a plasma based reactive ion etching module, achemical mechanical polishing module, or some combination thereof. In afirst configuration, the etching system 130 includes a wet bench whichperforms a chemical etching using a combination of acids, bases, andsolvents at a range of temperatures and concentrations. In a secondconfiguration, the etching system 130 includes an ion milling modulethat performs a physical removal of a portion of the thin filmsdeposited on the substrate at an extremely low pressure and using a highaccelerating potential in order to accelerate electrons impacting theneutral gas atoms with enough energy to ionize the gas atoms. In a thirdconfiguration, the etching system 130 includes a plasma based reactiveion etching (RIE) module based on a chemically reactive plasma at a lowpressure and an external electromagnetic field to remove one or morethin films of material deposited on the substrate. In a fourthconfiguration, the etching system 130 includes a chemical mechanicalpolishing (CMP) module that performs smoothening of one or more thinfilms of materials based on a combination of chemical and mechanicalforces. In some examples, the etching system 130 uses an abrasive andcorrosive chemical slurry along with a polishing pad and retaining ringto perform the chemical mechanical polishing on one or more thin filmsdeposited on the substrate patterned by the patterning system 110.

In some embodiments, the etching system 130 is based on a Gas ClusterIon Beams (GCIB) process that bombards a surface with a beam of highenergy nanoscale cluster ions. In the GCIS process, an expansion takesplace inside of a nozzle that shapes the gas flow and facilitates theformation of a jet of clusters. The jet of clusters passes throughdifferential pumping apertures into a region of high vacuum where theclusters are ionized by collisions with energetic electrons. The ionizedclusters are accelerated electrostatically to very high velocities, andthey are focused into a tight beam. In one example, an etch-compatiblefilm is partially removed by the Gas Cluster Ion Beams (GCIB) process bybombarding a surface of the etch-compatible film with a beam of highenergy nanoscale cluster ions.

FIG. 2A is a flowchart 200 illustrating the process of fabricatinggrating elements with a variable height performed by the manufacturingsystem 100 of FIG. 1, in accordance with one or more embodiments. Otherentities may perform some or all of the steps of the process in otherembodiments. Likewise, embodiments may include different and/oradditional steps, or perform the steps in different orders.

The manufacturing system 100 performs 210 a lithographic patterning of afirst photoresist deposited over a substrate and transfer the patterninto an underlying hard mask. As described above with reference to FIG.1, the patterning system 110 performs 210 a photolithographic patterningof a first photoresist deposited by the deposition system 120 over thesubstrate and transfers the pattern into an underlying hard mask. In oneexample, the patterning system 110 includes a convection oven fordehydration of the substrate at 150-200° C., a wafer spinner for coatingthe substance on the substrate, a mask aligner for defining thelithographic pattern on the substrate, and an exposure system fortransferring the lithographic pattern in the mask to the substrate. Insome embodiments, the patterning system 110 performs 210 a lithographicpatterning of a hard mask deposited over the one or more photoresistsprior to the lithographic patterning of the one or more photoresists.

The manufacturing system 100 performs 220 a deposition of a secondphotoresist on the patterned hard mask. As described above withreference to FIG. 1, the deposition system 120 deposits the secondphotoresist comprising one or more layers of SSQ derivatives, an organicpolymer, or some combination thereof. The deposition system 120 depositsthe second photoresist with a thickness ranging from few hundrednanometers to few microns.

The manufacturing system 100 performs 230 a lithographic patterning ofthe second photoresist to create a modified second photoresist with aplurality of heights relative to the substrate. As described above withreference to FIG. 1, the patterning system 110 performs 230 alithographic patterning of the second photoresist deposited by thedeposition system 120 over the patterned first photoresist. In someembodiments, the manufacturing system 100 performs 230 the lithographicpatterning of the second photoresist such that the modified secondphotoresist has a plurality of heights relative to the substrate in therange of few hundred nanometers to few microns.

The manufacturing system 100 performs 240 a pattern transfer into thesubstrate based on the first photoresist and the heights in the modifiedsecond photoresist to form a nanoimprint mold. The nanoimprint mold is astructure having a plurality of heights, and formed on the substrate bythe manufacturing system 100. As described below in conjunction withFIG. 3C, the manufacturing system 100 transfers the structure with theplurality of heights on the nanoimprint mold on to an organic material(e.g. nanoimprint resin), and the manufacturing system 100 forms anoptical grating on an optical waveguide. For example, the structure mayinclude a plurality of pillars (or rows in a 1D case) that each have arespective height measured from the substrate. And at least one, andgenerally more than one pillar, has height that is different from atleast one other pillar of the plurality of pillars. In someconfigurations, the etching system 130 performs 240 a partial removal ofa substrate made of Quartz using a Quartz etch recipe with an etch rateof few Angstroms per second to achieve a target height of ˜300 nm. Thequartz etch recipe could involve single or multitude of fluorinecontaining gases (e.g. CF₄, CHF₃, CH₂F₂, CH₃F, SF₆, NF₃, C₄F₈, C₄F₆,C₃F₈, F₂, ClF₃, HF, etc.) and other additives (e.g. Ar, He, Ne, Kr, O₂,N₂, N₂O, CH₄, SiCl₄, SiF₄, NH₃, etc.).

Note that conventional lithographic techniques such as photolithographyor electron beam lithography cannot modulate the heights of the modifiedsecond photoresist, and accordingly, the optical grating formed usingsuch conventional lithographic techniques cannot modulate the heights ofthe optical grating relative to the substrate. In contrast, themanufacturing system 100 modulates the duty cycles (e.g. 10 percent to90 percent), heights of the optical grating formed relative to thesubstrate, or some combination thereof. For example, the optical gratingmay include a plurality of pillars (or rows in 1D case) that each have arespective height measured from the substrate. And at least one, andgenerally more than one pillar, has height that is different from atleast one other pillar of the plurality of pillars.

FIG. 2B is a flowchart 202 illustrating the process of fabricatinggrating elements with a variable height and one or more duty cyclesperformed by the manufacturing system 100 of FIG. 1, in accordance withone or more embodiments. Other entities may perform some or all of thesteps of the process in other embodiments. Likewise, embodiments mayinclude different and/or additional steps, or perform the steps indifferent orders.

The manufacturing system 100 performs 210 a deposition of anetch-compatible film over a substrate. As described above with referenceto FIG. 1, the deposition system 100 deposits the etch-compatible filmof a target value of thickness over a substrate. The etch-compatiblefilm may be composed of materials including, but not restricted tometals or metallic compounds (e.g. TiO_(x), WC, W, Cr, TiN, etc.),silicon containing materials (e.g. SiO₂, Si₃N₄, SiON, SiC), carboncontaining materials (e.g. amorphous carbon, diamond like carbon, spinon carbon) epoxy resins (e.g. SU-8), novolac resins, etc. For example,the manufacturing system 100 performs 210 a deposition of a 300 nm Si3N4film over a substrate.

The manufacturing system 100 performs 220 a partial removal of theetch-compatible film to create a surface profile with a plurality ofetch heights relative to the substrate. As described below withreference to FIG. 7, the manufacturing system 100 performs 220 thepartial removal of the etch-compatible film to achieve a plurality etchheights in the range of few hundred nanometers to few microns relativeto the substrate. In some configurations, the manufacturing system 100uses an ion-beam assisted etching tool to partially remove theetch-compatible film at one or more locations.

The manufacturing system 100 performs 230 a lithographic patterning of aphotoresist deposited over the created profile in the etch-compatiblefilm to obtain at least one of the plurality of etch heights and one ormore duty cycles corresponding to the etch-compatible film depositedover the substrate. In one example, the patterning system 110 performs230 the lithographic patterning using a convection oven for dehydrationof the substrate at 150-200° C., a wafer spinner for coating thesubstance on the substrate, a mask aligner for defining the lithographicpattern on the substrate, and an exposure system for transferring thelithographic pattern in the mask to the substrate.

Note that conventional lithographic techniques such as photolithographyor electron beam lithography cannot modulate the etch heights of thephotoresist deposited over the created profile in the etch-compatiblefilm, and accordingly, the optical grating formed using suchconventional lithographic techniques cannot modulate the etch heights ofthe optical grating relative to the substrate. In contrast, themanufacturing system 100 modulates the duty cycles (e.g. 10 percent to90 percent), etch heights of the optical grating formed relative to thesubstrate, or some combination thereof. For example, the optical gratingmay include a plurality of pillars (or rows in 1D case) of theetch-compatible film that each have a respective height measured fromthe substrate. And at least one, and generally more than one pillar, hasheight that is different from at least one other pillar of the pluralityof pillars.

FIG. 2C is a flowchart 204 illustrating the process of fabricatinggrating elements with a variable height and one or more duty cyclesperformed by the manufacturing system 100 of FIG. 1, in accordance withone or more embodiments. Other entities may perform some or all of thesteps of the process in other embodiments. Likewise, embodiments mayinclude different and/or additional steps, or perform the steps indifferent orders.

The manufacturing system 100 performs 210 a deposition of anetch-compatible film over a substrate. As described above with referenceto FIG. 1, the deposition system 100 deposits the etch-compatible filmof a target value of thickness over a substrate. The etch-compatiblefilm may be composed of materials including, but not restricted to,epoxy resins (e.g. SU-8), novolac resins, etc. The manufacturing system100 performs 220 a partial removal of the etch-compatible film to createa surface profile with a plurality of depths relative to the substrate.In some configurations, the manufacturing system 100 uses an ion-beamassisted etching tool to partially remove the etch-compatible film atone or more locations. The manufacturing system 100 performs 230 adeposition of a second material over the profile created in theetch-compatible film. As described above with reference to FIG. 1, thedeposition system 100 deposits the second material of a target value ofthickness over the profile created in the etch-compatible film. Thesecond material may be composed of materials including, but notrestricted to, epoxy resins (e.g. SU-8), novolac resins, SSQderivatives, etc.

The manufacturing system 100 performs 240 a planarization of the secondmaterial to obtain a plurality of etch heights of the second material inaccordance with the plurality of depths in the profile created in theetch-compatible film. In one example, the manufacturing system 100performs a chemical mechanical polishing of the deposited secondmaterial to achieve a target value of thickness and surface roughness ofthe second material. The manufacturing system 100 performs 250 alithographic patterning of a photoresist deposited over the planarizedsecond material and a subsequent etching of the second material (withhigh selectivity to the first material) to obtain at least one of theplurality of etch heights and one or more duty cycles in the secondmaterial. In one example, the patterning system 110 performs 250 thelithographic patterning using a convection oven for dehydration of thesubstrate at 150-200° C., a wafer spinner for coating the substance onthe substrate, a mask aligner for defining the lithographic pattern onthe substrate, and an exposure system for transferring the lithographicpattern in the mask to the substrate.

Note that conventional lithographic techniques such as photolithographyor electron beam lithography cannot modulate the etch heights of thephotoresist deposited over the planarized second material, andaccordingly, the optical grating formed using such conventionallithographic techniques cannot modulate the etch heights of the opticalgrating relative to the substrate. In contrast, the manufacturing system100 modulates the duty cycles (e.g. 10 percent to 90 percent), etchheights of the optical grating formed, or some combination thereof. Forexample, the optical grating may include a plurality of pillars (or rowsin 1D case) that each have a respective height of the second materialmeasured from the etch-compatible film. And at least one, and generallymore than one pillar, has height that is different from at least oneother pillar of the plurality of pillars.

FIG. 3A-C illustrate a process 300 of creating grating elements with avariable height by the manufacturing system of FIG. 1, in accordancewith one or more embodiments. The process 300 of FIG. 3A-C may beperformed by the manufacturing system 100. Other entities may performsome or all of the steps of the process in other embodiments. Likewise,embodiments may include different and/or additional steps, or performthe steps in different orders.

The manufacturing system 100 performs 310 a deposition of one or morephotoresists on a substrate 302. For example, the manufacturing system100 performs a deposition of a hard mask 306 on the substrate 302. Themanufacturing system 100 performs 310 a deposition of a firstphotoresist 304 on the hard mask 306. The first photoresist 304 iscomposed of an organic material such as an imprint resist, a shieldresist, etc. In the example of FIG. 3, the first photoresist 304 is aSSQ derivative and the hard mask 306 is a metal layer such as Chrome,Nickel, and Aluminum etc.

The manufacturing system 100 performs 315 a lithographic patterning ofphotoresists deposited on the substrate 302. In one example, thepatterning system 110 uses a lithographic exposure to pattern the firstphotoresist 304. The etching system 130 selectively removes thelithographically exposed regions of the patterned photoresist.

The manufacturing system 100 performs 320 a lithographic patterning ofthe hard mask 306 deposited on the substrate 302. In one example, thepatterning system 110 uses a lithographic exposure to pattern the hardmask 306. The etching system 130 selectively removes thelithographically exposed regions of the patterned hard mask 306. Inalternate embodiments, the patterning system 110 uses a singlelithographic exposure to pattern the first photoresist 304 and the hardmask 306.

The manufacturing system 100 performs 325 a removal of the firstphotoresist 304. The manufacturing system 100 performs 335 a depositionof a gray-scale photoresist 332. The manufacturing system 100 performs340 a lithographic patterning of the gray-scale photoresist 332 using agray-scale mask 342. The gray-scale mask 342 is an optical componentthat selectively transmits ultra-violet radiation of different levels ofintensity to a gray-scale photoresist (e.g. AZ 9260) underneath thegray-scale mask 342. The gray-scale mask 342 modulates the amount ofexposure of ultra-violet radiation such that the gray-scale photoresistforms a plurality of heights relative to the substrate after adevelopment process during lithography. The gray-scale mask 342modulates the height of the developed gray-scale photoresist todifferent levels, which in turn is transferred on to an organic material(e.g. nanoimprint resin) to produce optical gratings with a plurality ofetch depths. In some configurations, the gray-scale mask 342 forms 2^(N)different heights of the gray-scale photoresist with ‘N’ number ofexposure and development process performed by the manufacturing system100. The gray-scale mask 342 is fabricated by the manufacturing system100 using methods including, but not restricted to, a laser ablationprocess, a layer-by-layer deposition, a layer-by-layer etching process,etc. More details about the fabrication of the gray-scale mask 342 aredescribed below in detail with reference to FIGS. 4-6.

The manufacturing system 100 performs 345 a partial removal of thepatterned gray-scale photoresist 332. The manufacturing system 100performs 350 a partial removal of the substrate 302. The manufacturingsystem 100 performs 355 a removal of the gray-scale photoresist 332 anda partial removal of the substrate 302. The manufacturing system 100performs 360 a removal of the hard mask 306 to form a nanoimprint mold358. As shown in FIG. 3C, the nanoimprint mold 358 has a plurality ofheights with reference to the substrate 302.

The manufacturing system 100 performs 365 a deposition of a nanoimprintresin 362 over the nanoimprint mold 358. The manufacturing system 100performs 365 the application of the nanoimprint resin 362 over anoptical waveguide 366. The manufacturing system 100 removes 370 thenanoimprint mold 358 in order to transfer the pattern in the nanoimprintmold 358 onto an optical grating 372 formed on the optical waveguide366. As described below with reference to FIG. 9, the optical grating372 is a grating element with a plurality of heights, one or more dutycycles, or some combination thereof, in waveguide displays used forapplications including, but not restricted to, near-eye-displays (NEDs),Head-Mounted Displays (HMDs), etc. Note that conventional lithographictechniques such as photolithography or electron beam lithography cannotmodulate the heights of the nanoimprint mold 358, and accordingly, theoptical grating formed using such conventional lithographic techniquescannot modulate the heights of the optical grating relative to thesubstrate. In contrast, the manufacturing system 100 modulates the dutycycles (e.g. 10 percent to 90 percent), heights of the optical grating372 formed, or some combination thereof.

FIG. 4 is an illustration of a laser ablation process 400 forfabricating a gray-scale mask 410 using the manufacturing system 100 ofFIG. 1, in accordance with at least one embodiment. The process 400 ofFIG. 4 may be performed by the manufacturing system 100. Other entitiesmay perform some or all of the steps of the process in otherembodiments. Likewise, embodiments may include different and/oradditional steps, or perform the steps in different orders. Thegray-scale mask 410 is an embodiment of the gray-scale mask 342described above with reference to FIG. 3B. The gray-scale mask 410selectively transmits ultra-violet radiation of different levels ofintensity to a photoresist underneath the gray-scale mask 410.

As shown in FIG. 4, the manufacturing system 100 deposits over a UVtransparent substrate 402 a metal 404 of a target value of thickness toform the gray-scale mask 410. The UV transparent substrate 402 may becomposed of materials including, but not restricted to, soda lime,quartz, fused silica, etc. The metal 404 may be composed of materialsincluding, but not restricted to, chrome, molybdenum, silver, gold, orany other material that can block ultra-violet radiation.

The laser 406 performs a scanning operation on the metal 404 by movingacross the X-Y plane to different locations with different speeds (e.g.along the X-direction and the Y-direction) at different time intervals.The manufacturing system 100 includes a controller (not shown here) thatcontrols the intensity and the speed of movement of the laser 406 toachieve a plurality of doses of laser exposure over the exposed area ofthe metal 404 resulting in a removal of different amounts of the metal404 across the exposed area. The laser 406 performs a partial erosion ofthe metal 404 at different locations to yield different levels ofopacity of the gray-scale mask 410. The laser ablation process 400achieves a smooth mask profile on the metal 404 resulting in a uniformvariation of ultra-violet radiation transmitted by the gray-scale mask410. In alternate embodiments, the manufacturing system 100 varies theopacity of the gray-scale mask 410 by varying the thickness of the metal404 deposited on the UV transparent substrate 402.

FIG. 5A-B is an illustration of a layer-by-layer deposition process 500of creating a gray-scale photomask 580 using the manufacturing system100 of FIG. 1, in accordance with one or more embodiments. The process500 of FIG. 5 may be performed by the manufacturing system 100. Otherentities may perform some or all of the steps of the process in otherembodiments. Likewise, embodiments may include different and/oradditional steps, or perform the steps in different orders. Themanufacturing system 100 performs the process 500 using, among severalother components, a UV transparent substrate 502, a photoresist 504, abinary photomask 506, and a UV-blocking material 532. Referring back toFIG. 3, the UV transparent substrate 502 is an embodiment of thesubstrate 302, the photoresist 504 is an embodiment of the firstphotoresist 304, and the binary photomask 506 is an embodiment of thehard mask 306. Referring back to FIG. 4, the UV-blocking material 532 isan embodiment of the metal 404.

The manufacturing system 100 performs 510 a lithographic patterning ofthe UV transparent substrate 502 deposited with the photoresist 504using the binary photomask 506. As described above with reference toFIG. 1, the patterning system 110 performs 510 a lithographic patterningof the photoresist 504 deposited by the deposition system 120 over theUV transparent substrate 502. In some embodiments, the manufacturingsystem 100 performs 510 the lithographic patterning of the photoresist504 such that the photoresist 504 has a thickness in the range of fewhundred nanometers to few microns.

The manufacturing system 100 performs 520 a development of thephotoresist 504. For example, the patterning system 110 performs 520 awet etching of the exposed areas of the photoresist 504 such that aportion of the photoresist 504 gets removed during the developmentprocess.

The manufacturing system 100 deposits 530 the UV-blocking material 532over the developed photoresist 504. As described above with reference toFIG. 1, the deposition system 120 deposits the UV-blocking material 532.The deposition system 120 deposits the UV-blocking material 532 with athickness ranging from few hundred nanometers to few microns.

The manufacturing system 100 performs 540 a lift-off of the developedphotoresist 504 resulting in a partial removal of the UV-blockingmaterial 532. The manufacturing system 100 performs 540 the lift-off ofthe developed photoresist 504 to form an intermediate gray-scalephotomask.

The manufacturing system 100 performs 550 a second lithographicpatterning of the photoresist 504 using the binary photomask 506 on theintermediate gray-scale photomask formed. As described above withreference to FIG. 1, the patterning system 110 performs 550 the secondlithographic patterning of the photoresist 504 using the binaryphotomask 506. In some embodiments, the manufacturing system 100performs 550 the second lithographic patterning of the photoresist 504such that the photoresist 504 has a thickness in the range of fewhundred nanometers to few microns.

The manufacturing system 100 performs 560 a development of thephotoresist 504. For example, the patterning system 110 performs 560 awet etching of the exposed areas of the photoresist 504 such that aportion of the photoresist 504 gets removed during the developmentprocess.

The manufacturing system 100 deposits 570 the UV-blocking material 532over the developed photoresist 504. As described above with reference toFIG. 1, the deposition system 120 deposits the UV-blocking material 532.The deposition system 120 deposits the UV-blocking material 532 with athickness ranging from few hundred nanometers to few microns.

The manufacturing system 100 performs 575 a lift-off of the developedphotoresist 504 resulting in a partial removal of the UV-blockingmaterial 532. The manufacturing system 100 performs 575 the lift-off ofthe developed photoresist 504 to form a gray-scale photomask 580.

In the example of FIG. 5B, the manufacturing system 100 forms thegray-scale photomask 580 with two lithographic patterning stepsresulting in four different levels (shown as levels 0, 1, 2 and 3) ofthe gray-scale photomask 580 with each level corresponding to thethickness of the UV-blocking material 532 deposited during the process500. Note that the process 500 may be repeated with more than twolithographic patterning steps to form the gray-scale photomask 580 witha target number of levels according to the target opacity of thegray-scale photomask 580. In the illustrated example, the manufacturingsystem 100 forms the gray-scale photomask 580 with four differentheights. In alternate examples, the gray-scale photomask 580 may includea plurality of pillars of the UV-locking material 532 that each have arespective height measured from the UV transparent substrate 502. And atleast one, and generally more than one pillar, has height that isdifferent from at least one other column of the plurality of pillars.The gray-scale photomask 580 is used to fabricate optical gratings withfour different etch depths (e.g. few hundred nanometers to a fewmicrons), one or more duty cycles (e.g. 10 percent to 90 percent), orsome combination thereof. Such optical gratings cannot be formed usingconventional lithographic techniques.

FIG. 6A-B is an illustration of a layer-by-layer etching process 600 ofcreating a gray-scale photomask 680 using the manufacturing system ofFIG. 1, in accordance with one or more embodiments. The process 600 ofFIG. 6 may be performed by the manufacturing system 100. Other entitiesmay perform some or all of the steps of the process in otherembodiments. Likewise, embodiments may include different and/oradditional steps, or perform the steps in different orders. Referringback to FIG. 5A, the manufacturing system 100 performs the process 600using, among several other components, the UV transparent substrate 502,the photoresist 504, the binary photomask 506, and the UV-blockingmaterial 532.

The manufacturing system 100 performs 610 a lithographic patterningusing the binary photomask 506 on the photoresist 504 deposited over theUV-blocking material 532 coated on the UV transparent substrate 502.Note that the process 600 includes the deposition of the photoresist 504directly on the UV-blocking material 532 unlike the process 500described above with reference to FIG. 5A.

The manufacturing system 100 performs 620 a development of thephotoresist 504. For example, the patterning system 110 performs 620 awet etching of the exposed areas of the photoresist 504 such that aportion of the photoresist 504 gets removed during the developmentprocess.

The manufacturing system 100 performs 630 a partial removal of theUV-blocking material 532 using the developed photoresist 504 as an etchmask. In one example, the manufacturing system 100 performs 630 thepartial removal of the UV-blocking material 532 based on a dry etchprocess (e.g. reactive-ion-etching, ion milling, etc.). Themanufacturing system 100 performs 630 the partial removal of theUV-blocking material 532 such that the thickness of the UV-blockingmaterial 532 is in the range of few hundred nanometers to few microns.The manufacturing system 100 performs 640 a selective removal of thedeveloped photoresist 504 to form an intermediate gray-scale photomask.In one example, the manufacturing system 100 performs 640 the selectiveremoval of the developed photoresist 504 based on a wet etching of thedeveloped photoresist 504.

The manufacturing system 100 performs 650 a second lithographicpatterning of the photoresist 504 using the binary photomask 506 on theintermediate gray-scale photomask formed. As described above withreference to FIG. 1, the patterning system 110 performs 650 alithographic patterning of the photoresist 504 deposited by thedeposition system 120. In some embodiments, the manufacturing system 100performs 650 the lithographic patterning of the photoresist 504 usingthe binary photomask 506 such that the photoresist 504 has a thicknessin the range of few hundred nanometers to few microns.

The manufacturing system 100 performs 660 a development of thephotoresist 504. For example, the patterning system 110 performs 660 awet etching of the exposed areas of the photoresist 504 such that aportion of the photoresist 504 gets removed during the developmentprocess.

The manufacturing system 100 performs 670 a partial removal theUV-blocking material 532 using the developed photoresist 504 as an etchmask. The manufacturing system 100 performs 675 the lift-off of thedeveloped photoresist 504 to form a gray-scale photomask 680.

In the example of FIG. 6B, the manufacturing system 100 forms thegray-scale photomask 680 with two lithographic patterning stepsresulting in four different levels (shown as levels 0, 1, 2 and 3) ofthe gray-scale photomask 680 with each level corresponding to the etchdepth after partial removal of the UV-blocking material 532 depositedduring the process 600. Note that the process 600 may be repeated withmore than two lithographic patterning steps to form the gray-scalephotomask 680 with a target number of levels according to the targetopacity of the gray-scale photomask. The manufacturing system 100 formsthe gray-scale photomask 680 with a plurality of heights which is usedto fabricate optical gratings with the plurality of heights, one or moreduty cycles (e.g. 10 percent to 90 percent), or some combinationthereof. Such optical gratings cannot be formed using conventionallithographic techniques. In alternate examples, the gray-scale photomask680 may include a plurality of pillars of the UV-locking material 532that each have a respective height measured from the UV transparentsubstrate 502. And at least one, and generally more than one column, hasheight that is different from at least one other column of the pluralityof columns.

FIG. 7 is an illustration of a process 700 of creating an opticalgrating with a variable height and/or duty cycles using themanufacturing system 100 of FIG. 1, in accordance with one or moreembodiments. The process 700 of FIG. 7 may be performed by themanufacturing system 100. Other entities may perform some or all of thesteps of the process in other embodiments. Likewise, embodiments mayinclude different and/or additional steps, or perform the steps indifferent orders.

The manufacturing system 100 deposits 705 an etch-compatible film over asubstrate. As described above with reference to FIG. 1, the depositionsystem 100 deposits the etch-compatible film of a target value ofthickness over a substrate. The etch-compatible film may be composed ofmaterials including, but not restricted to, epoxy resins (e.g. SU-8),novolac resins, etc.

The manufacturing system 100 performs 710 a location-specific partialremoval of the etch-compatible film according to a target range ofheights of an optical grating. In some configurations, the manufacturingsystem 100 uses an ion-beam assisted etching tool to partially removethe etch-compatible film at one or more locations. The manufacturingsystem 100 may also include a controller (not shown here) that generatesetch instructions in accordance with a target design of an opticalgrating and provides the etch instructions to the etching system 130 toperform a partial removal of the etch-compatible film.

The manufacturing system 100 deposits 720 a photoresist 715 on theetched etch-compatible film. The photoresist 715 is an embodiment of thefirst photoresist 304 of FIG. 3A. As described above with reference toFIG. 1, the deposition system 120 deposits the photoresist 715comprising one or more layers of SSQ derivatives, an organic polymer, orsome combination thereof. The deposition system 120 deposits thephotoresist 715 with a thickness ranging from few hundred nanometers tofew microns.

The manufacturing system 100 performs 730 a lithographic patterning ofthe photoresist 715. Note that the manufacturing system 100 performs 730the lithographic patterning of the photoresist 715 in accordance with atarget range of values of duty cycle of the optical grating. Forexample, the target range of values of duty cycles is from 10 percent to90 percent.

The manufacturing system 100 performs 740 a selective removal of theetch-compatible film using the lithographically patterned photoresist715 as an etch mask. In one example, the manufacturing system 100performs 740 the selective removal of the etch-compatible film based ona dry etching process (e.g. ion milling, reactive ion etching).

The manufacturing system 100 selectively removes 750 the patternedphotoresist 715 to form an optical grating with a variable height and/orone or more duty cycles. In the example of FIG. 7, the manufacturingsystem 100 forms the optical grating with an etch height 755, an etchheight 760, and an etch height 765 relative to the substrate. In someembodiments, each of the etch heights 755, 760, and 765 is a root meansquare (RMS) value of the height of the optical grating with respect tothe substrate, and are in the range of few hundred nanometers to fewmicrons. In the example of FIG. 7, the optical grating includes aplurality of pillars of the etch-compatible film that each have arespective height measured from the substrate. And at least one, andgenerally more than one pillar, has height that is different from atleast one other pillar of the plurality of pillars. Accordingly, theprocess 700 adjusts the shape, refractive index, height and/or dutycycle of the optical grating allowing for full control of thebrightness, uniformity, field-of-view, and efficiency of an image lightprojected to a user's eye.

FIG. 8 is an illustration of a process of creating an optical gratingwith a variable height and/or duty cycles using the manufacturing systemof FIG. 1, in accordance with one or more embodiments. The process 800of FIG. 8 may be performed by the manufacturing system 100. Otherentities may perform some or all of the steps of the process in otherembodiments. Likewise, embodiments may include different and/oradditional steps, or perform the steps in different orders.

The manufacturing system 100 deposits 805 an etch-compatible film over asubstrate. As described above with reference to FIG. 1, the depositionsystem 100 deposits the etch-compatible film of a target value ofthickness over a substrate. The etch-compatible film may be composed ofmaterials including, but not restricted to, epoxy resins (e.g. SU-8),novolac resins, etc.

The manufacturing system 100 performs 810 a location-specific partialremoval of the etch-compatible film according to a target range ofheights of an optical grating. In some configurations, the manufacturingsystem 100 uses an ion-beam assisted etching tool to partially removethe etch-compatible film at one or more locations. The manufacturingsystem 100 may also include a controller (not shown here) that generatesetch instructions in accordance with a target design of an opticalgrating and provides the etch instructions to the etching system 130 toperform a partial removal of the etch-compatible film.

The manufacturing system 100 deposits 820 a second material 815 on thepartially removed etch-compatible film and performs a partial removal ofthe second material 815. In one example, the manufacturing system 100performs a chemical mechanical polishing of the deposited secondmaterial 815 to achieve a target value of thickness and surfaceroughness of the second material 815. The second material 815 may becomposed of materials including but not restricted to, an epoxy resin, anovolac resin, or some combination thereof.

The manufacturing system 100 deposits 830 a photoresist 825 on thepolished surface of the second material 815. The photoresist 825 is anembodiment of the first photoresist 304 of FIG. 3A. As described abovewith reference to FIG. 1, the deposition system 120 deposits thephotoresist 825 comprising one or more layers of SSQ derivatives, anorganic polymer, or some combination thereof. The deposition system 120deposits the photoresist 825 with a thickness ranging from few hundrednanometers to few microns.

The manufacturing system 100 performs 835 a lithographic patterning ofthe photoresist 825. Note that the manufacturing system 100 performs 835the lithographic patterning of the photoresist 825 in accordance with atarget range of values of duty cycle of the optical grating. Forexample, the target range of duty cycles is in the range of 10 percentto 90 percent.

The manufacturing system 100 performs 840 a selective removal of thesecond material 815 using the lithographically patterned photoresist 825as an etch mask. In one example, the manufacturing system 100 performs840 the selective removal of the second material 815 based on a dryetching process (e.g. ion milling, reactive ion etching).

The manufacturing system 100 selectively removes the patternedphotoresist 825 to form an optical grating with a variable height and/orone or more duty cycles. In the example of FIG. 8, the manufacturingsystem 100 forms the optical grating with an etch height 822 and an etchheight 824 relative to the etch-compatible film deposited over thesubstrate. In some embodiments, each of the etch heights 822, and 824 isa root mean square (RMS) value of the height of the second material 815with respect to the etch-compatible film, and are in the range of fewhundred nanometers to few microns. In the example of FIG. 8, the opticalgrating includes a plurality of pillars of the second material 815 thateach have a respective height measured from the etch-compatible film.And at least one, and generally more than one pillar, has height that isdifferent from at least one other pillar of the plurality of pillars.Accordingly, the process 800 adjusts the shape, refractive index, heightand/or duty cycle of the optical grating allowing for full control ofthe brightness, uniformity, field-of-view, and efficiency of an imagelight projected to a user's eye.

Note that in the absence of the second material 815, the optical gratingformed by the process 800 will have an uneven surface at a region 850 ofthe optical grating that interfaces with air.

FIG. 9 is a diagram of a near-eye-display (NED) 900 that includescomponents fabricated using the manufacturing system of FIG. 1, inaccordance with one or more embodiments. The NED includes one or moredisplays 910 that include optical gratings with variable heights and/orduty cycles fabricated using the manufacturing system 100, in accordancewith an embodiment. The NED 900 presents media to a user. Examples ofmedia presented by the NED 900 include one or more images, video, audio,or some combination thereof. In some embodiments, audio is presented viaan external device (e.g., speakers and/or headphones) that receivesaudio information from the NED 900, a console (not shown), or both, andpresents audio data based on the audio information. The NED 900 isgenerally configured to operate as a VR NED. However, in someembodiments, the NED 900 may be modified to also operate as an augmentedreality (AR) NED, a mixed reality (MR) NED, or some combination thereof.For example, in some embodiments, the NED 900 may augment views of aphysical, real-world environment with computer-generated elements (e.g.,images, video, sound, etc.).

The NED 900 shown in FIG. 9 includes a frame 905 and a display 910. Theframe 905 includes one or more optical elements which together displaymedia to users. The display 910 is configured for users to see thecontent presented by the NED 900.

FIG. 9 is only an example of an artificial reality system. However, inalternate embodiments, FIG. 9 may also be referred to as aHead-Mounted-Display (HMD).

Additional Configuration Information

The foregoing description of the embodiments of the disclosure has beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A method comprising: performing a deposition of ahard mask over a substrate; performing a deposition of a firstphotoresist over the hard mask; performing a lithographic patterning ofthe first photoresist to form a pattern; performing a transfer of thepattern onto the hard mask; performing a deposition of a secondphotoresist on the patterned hard mask; performing a lithographicpatterning of the second photoresist to create a modified secondphotoresist with a plurality of heights relative to the substrate; andperforming a partial removal of the substrate based on the plurality ofheights in the modified second photoresist and the pattern defined bythe patterned hard mask to form a nanoimprint mold comprising at least aplurality of different etch depths and one or more duty cycles.
 2. Themethod of claim 1, further comprising: performing a transfer of apattern in the nanoimprint mold onto an optical waveguide, the transferof the pattern in the nanoimprint mold forming an optical gratingcomprising the plurality of different etch depths and the one or moreduty cycles.
 3. The method of claim 1, wherein the second photoresist isa gray-scale photoresist lithographically patterned using a gray-scalemask.
 4. The method of claim 3, further comprising: performing adeposition of a metal layer over a second substrate to fabricate thegray-scale mask; and adjusting a thickness of the deposited metal layerbased on an erosion process performed by a laser scanning the metallayer, the adjusted thickness of the deposited metal layer forming aportion of the gray-scale mask.
 5. The method of claim 3, furthercomprising: performing a deposition of a third photoresist over a secondsubstrate to fabricate the gray-scale mask; performing a lithographicpatterning of the third photoresist using a binary photomask; performinga deposition of a second material on the third photoresist, the secondmaterial configured to block ultra-violet radiation through thegray-scale mask; and performing a removal of the lithographicallypatterned third photoresist to form a portion of the second material onthe second substrate, the portion of the second material forming aportion of the gray-scale mask with a threshold number of layers of thesecond material.
 6. The method of claim 3, further comprising:performing a deposition of a second material over a second substrate tofabricate the gray-scale mask, the second material configured to blockultra-violet radiation through the gray-scale mask; performing adeposition of a third photoresist over the second material on the secondsubstrate; performing a lithographic patterning of the third photoresistusing a binary photomask; and performing a partial removal of the secondmaterial deposited on the second substrate, the partially removed secondmaterial forming a portion of the gray-scale mask with a thresholdnumber of layers of the second material.